Compact light weight autothermal reformer assembly

Abstract

A fuel gas-steam reformer assembly, preferably an autothermal reformer assembly, for use in a fuel cell power plant, includes a catalyst bed which is formed from a cylindrical monolithic open cell foam body. The foam body is preferably formed from a high temperature material such as stainless steel, nickel alloys and iron-aluminum alloys, or from a ceramic material. The foam body includes open cells or pores which are contained within the metal or ceramic lattice. The lattice is coated with a porous wash coat which serves as a high surface area substrate onto which catalysts used in the reformer are applied. The foam body has an inlet end into which a mixture of fuel, steam and air is fed to begin the reforming process. An inlet portion of the foam body may be provided with an iron oxide and / or noble metal catalyst and the remainder of the foam body may be provided with a nickel and / or noble metal catalyst. An advantage of including an autothermal reformer in a fuel processing system is the compactness of the autothermal reformer. The inclusion of the foam catalyst bed rather than the traditional catalyzed pellet bed allows the reformer to be made even more compact and light weight.

Description

[0001]This is a continuation of a application Ser. No. 09 / 321,390, filed 27 May 1999, now U.S. Pat. No. 6,797,244.TECHNICAL FIELD[0002]This invention relates to a fuel gas steam reformer assembly. More particularly, this invention relates to an autothermal fuel gas steam reformer assembly which employs an open cell foam catalyst bed that reduces the size and weight of the reformer assembly.BACKGROUND ART[0003]Fuel cell power plants include fuel gas steam reformers which are operable to catalytically convert a fuel gas, such as natural gas or heavier hydrocarbons, into the primary constituents of hydrogen and carbon dioxide. The conversion involves passing a mixture of the fuel gas and steam through a catalytic bed which is heated to a reforming temperature which varies depending upon the fuel being reformed. Catalysts typically used are nickel catalysts which are deposited on alumina pellets. There are three types of reformers most commonly used for providing a hydrogen-rich gas str...

AI Technical Summary

Benefits of technology

[0010]This invention relates to a fuel cell system autothermal reformer assembly which provides an enhanced catalyst and heat transfer surface area; is compact and light weight; and provides an enhanced gas mixing and distribution flow path. The catalyst bed structure of this invention is formed from a monolithic open cell foam core which is provided with a porous high surface area wash coat layer onto which the catalyst layer is deposited. The wash coat may be alumina, lanthanum-stabilized alumina, silica-alumina, silica, ceria, silicon carbide, or another high surface ceramic material. The choice of wash coat will depend on the operating parameters of the specific catalyst bed.

[0011]The monolithic gas flow component is a foam with interconnected open cells, the surfaces of which are catalyzed with a catalyst. The foam monolith has an entry end portion which is coated with a catalyst consisting of lanthanum-promoted alumina, calcium oxide, and an iron oxide catalyst which can also be treated with a small amount of platinum, paladium or rhodium for improved low temperature fuel gas ignition. As an alternative configuration, the entry end may include a catalyst of platinum, paladium or rhodium without the iron oxide catalyst. The remainder of the foam monolith is provided with a nickel, copper or zinc catalyst, or with such noble metal catalysts such as platinum, palladium, rhodium, or the like. The open cell foam, once wash coated, provides the high surface area base required in order to achieve the deposition of the high surface area catalysts needed to properly process the fuel gas. The open cell foam also provides an enhanced mixing and distribution gas flow pattern for gases passing through the monolith since the gases will flow both laterally and longitudinally through the structure. The open cell foam also provides high surface area heat transfer paths that contribute to a more turbulent gas flow that enhances heat transfer rates in systems utilizing the catalyst bed. Additionally, the high heat transfer provided by the foam can be continued into and through adjacent walls of the reactor so as to create a highly efficient heat transfer device that results in improved process temperature control and reduces the size and weight of the reformer for a given output level. The intervening walls may be flat plates or they may be cylindrical walls with heat transfer capabilities. The monolithic open cell foam catalyst bed may be bonded to the reformer catalyst bed walls by brazing, or any other appropriate mechanism which is suitable for the system in question. When a ceramic foam catalyst bed is employed, the catalyst bed will not likely be bonded to the reformer bed walls.

[0012]All surfaces to be catalyzed will be primed by means of a conventional wash coating process such as that provided by United Catalyst, W. R. Grace and Co., or Englehard Corp. The wash coating process produces a porous layer on all surfaces of the foam, which layer forms a base for the catalyst coating. It will be understood that the interstices as well as the outside surfaces of the open cell foam monolith are wash coated and are also catalyzed. Since the catalyst beds are of minimal size and weight, they are especially suited to vehicular applications where size and weight are critically important, and because vehicle applications require rapid start-up capability that is closely dependent on the size and weight of the components. Small, light weight catalyst and reactant beds can be rapidly heated with a minimum energy input.

Problems solved by technology

Autothermal reformers are often used when higher operation temperatures are required for the reforming process because the fuel to be processed is more difficult to reform.

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